Sites and Site Collections

A site collection is the technical unit SharePoint uses to group related sites together, sharing a single top-level URL, a common set of site collection administrators, and one storage quota. In the modern SharePoint experience, every new site you create — whether a team site backed by an Microsoft 365 Group or a standalone communication site — is automatically its own site collection with its own URL, unlike the classic model where administrators built deep subsite hierarchies under one shared site collection.

Classic SharePoint encouraged deep nesting, where a top-level portal site contained subsites for every department, and those subsites contained further subsites, all inheriting permissions and navigation from the parent unless explicitly broken — a structure that became brittle and hard to reorganize as companies grew. Modern SharePoint instead favors flat, independent sites (each its own site collection) associated together through hub sites, which add shared navigation, a common theme, and associated search scoping without forcing a rigid parent-child permission hierarchy.

A hub site is a designated site that other sites register to, inheriting its top navigation bar, theme, and logo, and gaining a combined search experience that surfaces content across all associated sites in one query — for example, a 'Marketing' hub might link together the Campaigns site, the Brand Assets site, and the Events site so employees browsing any one of them see the same navigation bar linking to the other two. Only a SharePoint administrator or a delegated hub-site owner can register a site to a hub, and a site can belong to only one hub at a time.